1. Field of the Invention
This invention relates to the use of water-insoluble thermoplastic materials, especially recycled plastics, as a binder and fuel source in the recycling of iron oxides, such as flue dust, in the steelmaking process.
2. Description of Related Prior Art
In the basic oxygen furnace steelmaking processes, and in the electric furnace process, hot, dust-laden gases are generated during the production of liquid steel. The hot gases are evacuated from the steelmaking vessel through a large duct and then cooled to remove the particulate matter. Gas cleaning systems in current use include both wet systems (e.g. venturi scrubbers) and dry systems (e.g. electrostatic precipitators). Dust also can be separated in a hot cyclone. In the wet dust-collection system, water is used to wash the particulates from the gas stream, and the resulting dust-laden water then is further processed to concentrate the solid particles into a sludge containing as much as 50% water by weight. In the dry collection systems, the particulates are collected as a dry dust. In either case, the collected particulates may contain about 55% total iron on a dry basis, with most of the dust in the form of iron oxide. Such dust or sludge generally is disposed in a landfill.
It is known to use synthetic or naturally occurring thermoplastic substances as bonding materials for metallic additives, such as alloying metals, in steelmaking. For example, Frazer U.S. Pat. No. 2,888,342 discloses employing synthetic or naturally occurring thermoplastics as bonding agents for alloying additives such as chromium, silicon, manganese, vanadium, titanium, tungsten, molybdenum, nickel, copper, etc. for addition to ferrous metals in the production of alloy steels and cast iron. Wood rosin is the preferred bonding material.
Lang et al. U.S. Pat. No. 3,644,113 discloses water-soluble graft copolymers of acrylic acid and methyl cellulose, and water-soluble salts thereof, as binders in the pelletization of minerals and ores, such as taconite.
Dingeman et al. U.S. Pat. No. 5,000,783 discloses, as a binder for pelletizing mineral materials, a modified starch and a water-dispersible polymer such as water-dispersible natural gums, pectins, cellulose derivatives, vinyl and acrylic polymers, such as acrylamide, acrylic acid, vinyl alcohol and vinyl acetate, and mixtures thereof.
Rosen et al. U.S. Pat. No. 4,802,914 discloses a method for agglomerating mineral ores comprising commingling a mineral ore concentrate with a binding amount of a water-soluble, high molecular weight polymer such as water-soluble polyacrylamide based polymers.
Clegg et al. U.S. Pat. No. 4,040,818 discloses the use of phenol-formaldehyde compositions as binders in the formation of a briquette containing Mg particles.
Ranke U.S. Pat. No. 3,898,076 discloses the production of alloying briquettes containing alloying materials such as ferro-manganese, ferro-vanadium, ferro-titanium, ferro-columbium, ferro-silicon, silico-manganese, calcium, boron, lithium, magnesium, chromium, zirconium and tungsten, together with a binder consisting of a mixture of a refined paraffin wax and a copolymer of an alkylene compound having 2 to 4 C atoms and a vinyl ester of a 1- to 6-C saturated monobasic aliphatic carboxylic acid, such as an ethylene/vinyl acetate resin copolymer.
Japan Patent Document No. 80-27,687 discloses the addition of 0.1-20 ppm of polyacrylamide binder and aluminum sulfate to a waste scrubbing solution containing Mn dust from an electric furnace.
None of these prior art patents shows the use of water-insoluble thermoplastics as binders for recycling waste particulate iron oxide.